Fluid circulating arrangement for hydraulic pressure systems



Oct. 13, 1953 E H, SCHANZUN 2,655,111

FLUID CIRCULATING ARRNGEMENT FOR HYDRAULIC PRESSURE SYSTEMS' Filed Dec.29, 1948 Patented Oct. 13, 1953 FLUID CIRCULATING ARRANGEMENT FORHYDRAULIC PRESSURE SYSTEMS Ernest H. Schanzlin, Clevelanch- Ohio,assignor to Borg-Warner Corporation, Chicago, Ill., a. corporation ofIllinois Application December 29, 1948, Serial No. 67,806

7 Claims. (Cl. 103-11) circulating arrangement for a hydraulicpressuresystem.

While the present invention is adapted for application in many andvarious uses, as will be evident from the following description, thisinvention is particul-arly suited for use in aircraft uuid controlsystems where the problem of oil congealment is especially acute and theinvention is therefore illustrated and described as applied in a fluidcontrol system for adjusting the pitch of an aircraft propeller.

ln certain types of aircraft the propeller pitch is automaticallyadjusted by varying the oil pressure on a controlpiston associated withthe propeller. Normally, this oil pressure is supplied i'rom a pumpdriven from the -aircraft engine, the pressure supplied being controlledthrough a suitable governor and distributor valve arrangement, wellknown in the art. Since it is desirable to provide a mechanism forfeathering the propeller in the event of engine failure and consequentnon-operation of the engine driven pump, one practice is to provide asecond pump which may be electrically driven, and which is operableindependently of the operation of the aircraft engine. It has been foundin practice that because this second pump is operated onlyintermittently, and indeed ordinarily is operated only under emergencyconditions, the oil in the second pump and associated Vlines may thickenand congeal due to cold and thus prevent the pump from operatingeffectively. Furthermore, the relief valve associated with the secondpump being also infrequently operated and Ibeing subject to the samecold as the pump may fail to operate at the required pressure due tothickening of the oil therein with consequent damage to the system.

An object of the present invention is to provide a new and effectivefluid control system so arranged as to prevent disabling of the systemdue to thickening or congealment of the oil.

Another object of the present invention is to provide a fluid controlsystem wherein a sufcient circulation of oil through the system isprovided in the normal operation thereof to prevent congealment of theoil.

A further object of the present invention is to provide a relief valveof improved design having a by-pass arrangement permitting circulationof duid therethrough at a low pressure, but arranged so as to seal theby-pass at a iiow level substantially less than that required to openthe relief valve.

In accordance with one embodiment of lthis invention a Huid controlsystem may be provided incorporating a primary pumping circuit having anormally operative pump connected w a iiuid supply and a utilizationdevice, and an auxiliary circuit including a-second pump connected -tothe same fluid supply and to the utilization device and ordinarilyoperative only upon failure of the rst pump. The system includes meansfor diverting a portion of the duid flow from the normally operativepump into the auxiliary pumping circuit Ito maintain a small ow of uidthrough the auxiliary pumping circuit. The system also includes a reliefvalve associated with the second pump and having a by-pass passagetherethrough permitting flow of iluid at a low rate but arranged toclose upon actuation of the second pump to prevent loss of pressure.

Other objects and advantages of the present invention will be apparentfrom the following detailed description taken in conjunction with -thedrawing wherein the single figure is a schematic representation of afluid control system in accordance with this invention, the relief valvebeing shown in axial section.

The fluid control system shown in the drawing is arranged to supply oilunder pressure from a supply tank 5 to a utilization device t, which maybe the pitch control mechanism of an aircraft propeller. In the normaloperation of this system, the iiuid pressure is provided by a pump 'lwhich may be driven by the aircraft engine (not shown). In the event ofnon-operation of the aircraft engine and consequent non-operation of thepump l, fluid pressure may be supplied from a secondary or auxiliarypumping circuit comprising a pump 8 connected to the supply tank 5 by aconduit t and connected to the utilization device 6 by a second conduitit. This second pump B is intended to be operated independently of theoperation of the aircraft engine and may be thus operated by an electricmotor (not shown). A check valve Ill may be connected in the conduitylll to prevent application of oil pressure from the pump l to the pumpt through the conduit lll. This check valve may of course be eliminatedWhere connection is made directly to the utilization device 6 and notthrough conduit I8, which connects the pump l to the device 6. It mayalso be eliminated where it is desired to permit pressure to be suppliedto the pump 8 from the pump l to establish a back flow through the pump8. This latter arrangement is particularly desirable where the pump 8 isof the pressure loaded type and consequently permits a relatively largeback flow around -the .bearings when pressure is not applied thereto.Under such circumstances the oil from the supply tank 5, which isusually the oil supply of the engine and -is consequently hot,'wi1lprevent freezing of the oil in the pump 3 and associated conduits 8 andIII. On the other hand, the loss of pressure due to leakage through the-pump 8 when in non-operatin'g condition may be difficult to controland4 suillciently great to represent a substantial decrease inefficiency in the primary pumping circuit comprising the pump 1. In suchcase the check valve I I is desirable.

In accordance with usual practice, the pump 8 has associated therewith arelief valve I2 which is arranged, in well known manner, to open at apredetermined pressure level to prevent damage to the system. In theembodiment illustrated a passage I4 is provided in the pump 8 andextends from the discharge side of the pump 8 to the inlet chamber |3 ofthe relief valve. A second passage I5 extends from the discharge side ofthe relief valve to the inlet side of the pump 8 so as to discharge intothe conduit 8 and back to the supply tank 5.

Because the relief valve I2 is required to operate only infrequently,the oil therein may congeal due to cold and thus when the pressure fromthe pump 8 exceeds the predetermined, desired level, the relief valvemay fail to operate, with consequent damage to the system. In accordancewith this invention, congealing of the oil in the relief valve isprevented by maintaining, during the normal operation of the fluidcontrol system, a definite circulation of hot engine oil from the supply5 through the relief valve. Thus, a conduit I8 has one end connected tothe inlet chamber I3 of the relief valve and the other end connectedthrough a check valve I1 to the conduit I8 which connects the pump 1 tothe utilization device 6, the conduit I8 being thus connected to thedischarge side of the pump 1. The check valve I1 has a restrictedorifice 28 adjacent its inlet end, that is, the end connected to theconduit I8, whereby a fractional part of the fluid flow through theconduit I8 is diverted into the conduit I8, the check valve I'I beingarranged to permit flow in the direction from the conduit I8 to therelief valve I2 but to prevent flow in reverse direction.

Referring now specifically to the relief valve construction of thisinvention, it will be seen from -the drawing that the relief valvecomprises an elongated housing 2| suitably secured to the pump 8 andhaving a cylindrical bore 22. A combination valve seat and dash potsleeve 23 is located in the right end portion of the bore 22, as viewedin the drawing, and is provided with suitable apertures 25 and 28,adjacent the right end of the sleeve 23 and on opposite sides thereof,the apertures 25 and 28 communicating with the passage I4 and theconduit I5, respectively. 'I'he right end of the sleeve 23 is closed toform a dash pot chamber 28 in which is journaled a piston 28 formed atthe right end of a stem 21 of relief valve 30. The particularconstruction and operation of this dash pot feature of the relief valveforms no part of the present invention and is described in more detailin U. S. Patent No. 2,351,512 to Ray G. Holt, issued June 13, 1944.

The relief valve 30 includes a tubular body portion, indicated at 3|,which tapers sharply at 32 to form the valve disc portion which seats onthe left end of the combination valve seat and dash pot cylinder 23.'Ihe tapered portion 32 has integrally formed therewith the stem 21 tothe right end of which is fixed the dash pot piston 28. Intermediate thepiston 28 and the tapered portion 32 are a plurality of radiallyextending spokes 34 which maintain the alignment of the valve 38 whilepermitting passage of fluid to the left through the relief valve inletchamber I3. The relief valve 38 is held normally closed by a helicallycoiled spring 38 positioned within the left portion of the bore 22, theright end of the spring 38 bearing against'a spring guide 31 seated onthe left end of the tubular portion 3| of the relief valve 30. The leftend of the spring 38 is lreceived in an elongated adjusting cap 33, thebody portion of which extends into and engages a suitably threadedportion 38 of the bore 22. Sealing ring 48 is associated with the cap 38to prevent leakage and a locking nut 4I is threaded on the left portionof the periphery of the cap 33 to secure the cap in position after therequired spring pressure has been established by threading the cap intoor out of the bore 22. When the pressure on the inlet side of the reliefvalve exceeds the oppositely directed pressure of the spring 38, therelief valve will open provided the oil therein has notthickened so muchas to prevent movement'of the valve 30 at this pressure.

In accordance with this invention, a by-pass path is provided throughthe relief valve from the inlet end thereof to the discharge end, thispath being maintained normally open to peiimit a passage of fluidthrough the relief valve, the fluid being supplied from the pump 1through conduit I8. It will be noted that the inwardly tapered portion32 forming the valve disc has formed therein a small aperture 45 whichextends from the inlet chamber side of the relief valve 30 to theinterior of the cylindrical body portion 3| thereof. Within thiscylindrical body portion 3| is located a normally open check valveassembly including a sleeve-like valve seat 43 which is retained in thecylindrical portion 3| by a split-ring 41 positioned at the left endthereof and which is sealed to the inner wall of the cylindrical bodyportion by a packing washer 43 received in an annular groove 48 formedin the periphery of the valve seat. A valve 50 of generally cylindricalform is associated with the valve seat 48 and located in the cylindricalbody portion 3| of relief valve 38. being slidably supported therein atits left end by an integrally formed, reduced portion 5| thereofjournaled within the sleeve 48, and at its right end by an integrallyformed flanged portion 52. The valve 58 is resiliently held away fromthe seat 48 by a helical spring 53, the left end of which bears againstthe right side of the sleeve 48 and the right end of which bears againstthe left side of the flanged portion 52 of the valve 5l. It will benoted that the flanged portion 52 has formed in the periphery thereof atransversely extending groove 54 and having a depth greater than thethickness of the flanged portion 52. A plurality of such grooves may beformed in the periphery of the flange 82 and cooperate to provide aplurality of passages through the flanged portion of the valve 58. Asecond passage is formed by a centrally disposed aperture 55 in thereduced portion 5I of the valve 50 and an angularly extending aperture58 connected thereto and extending to the right therefrom.

When the check valve is in its normally open position, as shown; theentrance to the aperture 58 is open. When the check valve closes byseat- .only to the respective positions of the parts as shown in thedrawing.

From the foregoing it will be evident that in the normal operation ofthis fluid control system there exists a passage from the discharge sideof the normally-operating pump 1 through the orilice-20, the check valveI1 and the conduit I6 to the inlet side of the relief valve I2. From theinlet chamber I of the relief valve I2, a further passage is providedthrough the aperture 45, the grooves 54, the annular chamber `definedbythe inside wall of the cylindrical body portion SI and the peripheryof the valve 50, and the passage formed by the connecting apertures 55and 55 formed in the reduced left portion 5l of the valve 50. 'I'hislast passage connects through an axially extending aperture 51 formed inthe spring retaining member 31 to the discharge passage I5 of the reliefvalve, this discharge passage I5 connecting in turn with the conduit 9which leads to the supply tank 5. It will be evident also that a certainamount of fluid pressure supplied from, the pump 1 through the conduitI6 to the inlet chamber of the relief valve I2 is applied through thepassage M to the discharge side of the normally non-operating pump il.Such leakage as may exist in this pump may be utilized to provide acirculatory path back through the pump from the discharge to the inletside and therefrom baclr to the tank 5.

ll'pon actuation of the pump d, the check valve tt immediately closesdue to the increased dow through the orifice 45 in the disc 3l of therelief valve, the spring t3 associated with the valve 5t being selectedto provide only sufficient pressure to hold the valve open against asmall flow such as provided by the pump l and diverted through the orice2U. Closing of relief valve 5U prevents loss of pressure during theoperation of pump t. dit the same time, the checlr` valve il closes andthe check valve il opens permitting now of fluid through the conduit IIIfrom the pump 8 to the utilization device t.

Upon the pressure supplied by the pump Il enceeding a predeterminedlevel, the relief valve it opens, that is the valve 3U moves to the leftaway from the valve seat 23 against the pressure of the spring ct. Thispermits the pump d to discharge through the relief valve back into thesuction line it connected to the tank 5. The discharge path from theinlet chamber VI3 includes the annular chamber defined by the peripheryof the body portion 3d and the inner wall of" the housing tl, that is,the bore 22, and the discharge passage i5, which connects to the inletside of the pump 8.

lt will be evident from the foregoing that in accordance with thisinvention, in the normal `operation of the fluid supply system a smallamount of oil is constantly circulated through the auxiliary pump t,relief valve i2, and associated connecting lines. By properly selectingthe diameter of the orifice with respect to the pressure supplied by thepump l, this circulatory flow may be made sufllcient to avoid any dangerof oil congealing in the less frequently used auxiliary pumping circuit.At the same time loss of pressure due to provision of this circulatingarrangement is held to a minimum in the case of the pri mary pumpingcircuit and actually substantially eliminated where the pump 8 isoperated.

"Where herein the various elements of the structure disclosed have beenreferred to as being located in a right or a left position, it will beunderstood this is done solely for the purpose of facilitatingdescription and such references relate While this invention has beenshown and described in conjunction with a fluid flow control system foraircraft, it will be understood that it is not limited to suchapplication and that many .changes and modifications may be made in thestructure disclosed without departing from the spirit or scope of thepresent invention.

l. In a fluid control system including a fluid supply, a first pumpconnected to said supply, a positive displacement type pump connected tosaid supply and arranged to be operable in the event of non-operation ofthe first pump. said positive displacement pump being of the typeallowing some reverse flow of fluid under pressure when said pump is notoperating, and by-pass means for circulating back through said positivedisplacement type pump a fractional quantity of the fluid supplied bysaid first pump during operation of said first pump.

2. In a fluid control system, a fluid supply, a primary pumping circuitincluding a first pump connected to said fluid supply, an auxiliarypumping circuit including a second positive displacement type pumpconnected to said fluid supply, and means for diverting a portion of thefluid flow from the primary pumping circuit into said auxiliary pumpingcircuit to maintain a flow of fluid through said secondary pumpingcircuit.

3. .d nuid control system in accordance with claim 2 wherein saiddiverting means includes a conduit having one end connected in saidprimary pumping circuit and the other end connected in the auxiliarypumping circuit, said conduit having a restricted orifice at the endconnected to the primary pumping circuit to cause diversion of only afractional part of the fluid delivered by the first pump.

4. A fluid control system in accordance with claim 2 wherein saiddiverting means includes a conduit having one end connected in saidprimary pumping circuit and the other end connected in the auxiliarypumping circuit, said conduit having a restricted orifice at the endconnected to the primary pumping circuit to cause diversion of only afractional part of the fluid delivered by the first pump, and a checlrvalve adjacent said orifice effective to prevent fluid flow from theauxiliary pumping circuit through said orifice.

5. d. fluid .control system according to claim 2 wherein a relief valveis associated with said second pump and connected to discharge into saidfluid supply, and means associated with said reliefl valve forpermitting a restricted flow of fluid through said relief valve at apressure less than i that developed by the second pump.

d. A fluid control system according to claim 2 wherein a relief valve isassociated with said second pump and connected to discharge into saidfluid supply, valvey means associated with said relief valve forpermitting a restricted flow of fluid through said relief valve at apressure less than that developed by said second pump, said valve meansbeing arranged to close upon actuation of said second pump tending tocreate an increased flow through said relief valve.

7. A fluid circulating arrangement for a hydraulic pressure system ofthe type including a fluid supply, a primary pump connected to deliverfluid from said supply and a secondary or standby pump of the positivedisplacement type connected for delivering fluid from said supply 7 8 inthe event .of nonoperation of :aid rst mism. References Cited in theiiieof this patent said standby pump being of the ype perm ng reverseiiow oi' liquid under pressure therethrough STATES PATENTS when saidstandby pump is not being operated, Number Name Date said circulatingarrangement including means 5 1,897,432 Klotzman Feb. 14. 1933 fordiverting a portion of the i'iuid now from the 22115370 Ernst et al Aug,13, 1940 primary pump into the auxiliary pump -to cause 2'243'354Trautman MBS' 27, 1941 a reverse now oi' a fractional quantity of the21255550 Fieber et al Sept. 9, 1941 nuid supplied by said firstpumpthrough said 21312377 Campbell Mar. 2, 1943 secondary or standbypump whereby congealing lo 2'366'388 Crosby Jan. 2, 1945 of the num 1nsaid standby pump :s mimmized. 2,420,890 MacDufr my 2o, 1947

